Massachusetts has replaced California at the top of the Energy Scorecard Top 10, which measures the states' efforts to plan and implement efficient energy policies.

According to the American Council for an Energy-Efficient Economy (ACEEE), which maintains and publishes the list, the six most improved states are Michigan, Illinois, Nebraska, Alabama, Maryland and Tennessee.

The Scorecard ranks the states based on metrics that capture best practices and recognize leadership in energy-efficiency policy and program implementation, according to the ACEEE.